This invention relates to apparatus for, and methods of, providing a hip prosthesis. More particularly, the invention relates to apparatus for, and methods of, providing a hip prosthesis with optimal stability over extended periods of time.
Failure of femoral components is a recognized concern. Such hip failures have occurred for a number of different reasons. For example, individuals have suffered hip failures from awkward falls and particularly falls as a result of advancing age. Until relatively recently, individuals suffering hip failures have often been unable to walk and have often been confined to wheelchairs.
In recent years, apparatus has been developed, and techniques have been developed and refined, for implanting hip prostheses. Such apparatus and techniques have involved the insertion of a prosthesis in a cavity in a patient""s femur and the bonding of the prosthesis to the femur. To improve bone quality and long term prosthesis fixation, bone particles have been inserted into the cavity and a binder has been disposed between the particles and the prosthesis in an attempt to unify them.
The hip prostheses of the prior art have been far from uniformly successful. For example, as many as ten percent (10%) of the hip prostheses have had to be repeated more than once because previous prostheses have not been successful. The failures in the hip prostheses have occurred for various reasons. One primary reason has been that the bone fragments have not been tightly packed in the femur cavity which receives the prosthesis. This has created voids in the cavity. The voids cause the bone cement to be unsupported and to crack when a force is exerted by the patient on the prosthesis as by standing, walking or running.
U.S. Pat. No. 5,192,283 issued to Robin J. M. Ling, Graham A. Gie, W. E. Michael Mikhail, James M. Elting and Tom J. J. II. Sloof on Mar. 9, 1993, for a xe2x80x9cSystem For Performing Hip Prosthesis Revision Surgeryxe2x80x9d is typical of the recent prior art. It involves problems which have caused failures in hip prostheses. One problem has been that the bone fragments have not been tightly packed in the cavity in the femur. This has created voids which constitute positions of weakness where failures in the prostheses have occurred.
Apparatus for, and methods of, preparing hip prosthesis implantation overcome the difficulties indicated above by packing the bone fragments tightly and substantially uniformly in a cavity in a patient""s femur. Such apparatus and methods have been disclosed and claimed in U.S. Pat. No. 5,910,172 issued to me on Jan. 8, 1999, for xe2x80x9cApparatus For, and Method of, Preparing Hip Prosthesis Implantation.xe2x80x9d The apparatus and methods disclosed and claimed in U.S. Pat. No. 5,910,172 then cause the bone fragments to become bonded to one another and to the femur when a binder is disposed between the prosthesis and the bone fragments close to the femur. As a result, forces applied to the femur become distributed substantially uniformly throughout the femur, the prosthesis and the bone fragments. Since these forces are substantially uniformly distributed throughout the femur cavity, the forces at such positions will be below those which produce failures in the prosthesis.
In one embodiment of the invention disclosed and claimed in U.S. Pat. No. 5,910,172, each tamp in a sequence has a collar at a progressively increased distance from the bottom of a cavity in a femur relative to other tamps in the sequence. The collar on each tamp has progressively increased dimensions relative to collars on other tamps to provide a snug fit of such collar against inner walls defining the femur cavity. Bone particles are also disposed in such cavity.
After the insertion of each tamp into the cavity, such tamp is driven into the cavity to pack the bone fragments in the cavity against one another, the collar and the femur inner walls. Such tamp is then removed from the cavity and the next tamp in the sequence is inserted, and driven, into the cavity. The distance for driving each tamp into the cavity may be defined by a coincidence between a marking on such tamp and the top of the femur.
When the last tamp in the sequence is removed from the cavity, the prosthesis is inserted into the cavity. The cavity is then filled with a binder which permeates the space between the bone particles through only a limited distance because of the tight packing of the bone particles. The prosthesis is slightly narrower than the last tamp so that a thin layer of the binder is formed between the prosthesis and the bone fragments. The binder hardens against the prosthesis and the bone particles to retain the prosthesis fixedly in the cavity.
This invention provides an improvement over the apparatus and method disclosed and claimed in the ""172 patent. The apparatus and method of this invention provide for an enhanced centralizing of the prosthesis in the femur cavity in which the prosthesis is disposed. In this way, the ability of the femur to withstand forces applied to the femur is enhanced. This substantially increases the time in which the prosthesis remains substantially implanted in the femur.
In a preferred embodiment of the invention, surface irregularities are removed from the inner wall of a femur cavity, preferably tapered. A tamp having an opening and a socket (with a particular configuration at the bottom end of the opening) is disposed in the femur cavity. The tamp may be one of a plurality of tamps each having a different length for the opening.
A guide, one of a plurality, disposed in the tamp opening has the particular configuration at an intermediate position to fits snugly in the opening. The guide has a collar which cooperates with the tamp socket to limit the movement of the guide into the tamp. A working portion of each guide below the collar has a bulbous shape which is tapered in accordance with the femur taper. Bone fragments between the guide working portion and the femur inner wall are packed against the inner wall when the tamp, and the guide movable with the tamp, are driven into the femur cavity. Numerals on the guide adjacent a slot in the tamp indicate the disposition of the guide in the tamp. Guides with working portions of progressively increasing lengths are disposed sequentially in progressive ones of the tamps to pack bone fragments at progressively increasing heights in the femur cavity against the cavity inner wall.
When the last one of the tamps and the last one of the guides have been removed from the cavity, a prosthesis having dimensions slightly less than the femur cavity dimensions is disposed in the cavity. A binder disposed in the cavity in the space between the inner wall of the femur cavity and the prosthesis binds the prosthesis to the femur.
In one embodiment, the tamp socket is an opening and the guide collar fits into the tamp opening to limit the movement of the guide into the tamp. In a modification, the tamp socket is disposed in a press fit on the guide collar to limit the movement of the guide into the tamp.